In recent years and continuing, data transmission rates between LSI chips/packages or between LSI and memory or storage go on increasing in the technological field of supercomputers or servers. Along with the increase of data transmission rates, serious issues such as degradation in signal waveforms and increase of power consumption become conspicuous in the conventional electric interconnects. To solve theses issues, optical interconnection using broadband optical transmission channels has been attracting attention as a new interconnection medium to realize a high-capacity data transmission at less power consumption.
In inter-board LSI connection making use of optical interconnection, many optical devices including light-emitting devices for converting electric signals to optical signals and photosensitive devices for performing opposite functions are arranged on a board. It is proposed to mutually connect these optical devices using optical transmission media such as fiber optic cables or optical waveguides. To allow expansion and maintenance of hardware systems in supercomputers or servers, LSI-mounting boards are attached to or detached from a system. It is desired that optical transmission media (paths) are also connected to or disconnected from the system during the system expansion or system maintenance. For this reason, there is demand in the technological field of optical interconnects to develop not only optical devices or optical transmission media, but also plug-in optical connectors.
Optical interconnections of supercomputers or servers have a huge number of optical transmission paths. Many inventions have been made on multi-fiber optical connectors for mutually connecting multi-channel transmission paths mainly in the fiber optic telecommunications field. A widely used standard of multi-fiber optical connector is a mechanical transferable (MT) ferrule-based connector which is of a direct contact type to bring optical fibers to face-to-face contact with those of a counterpart connector. See, for example, Patent Document 1 listed below. Many optical fibers are aligned in a MT ferrule at a prescribed pitch. Two facing ferrules are positioned with respect to each other using a guide pin furnished in one of the ferrules and a guide hole formed in the other ferrule. This method can bring a bundle of optical fibers of multi-core fiber optic cables to direct contact with each other at a time and at a low loss during connection.
However, applying a telecommunication-type MT ferrule-based connector to optical interconnection using a huge number of connectors will generate high cost. In a MT ferrule, optical fibers projecting from the front end of the ferrule are cut into a uniform length so as to slightly project from the front end at a constant length, for the purpose of reducing fluctuation in connection loss due to the unevenness of the fiber projection. In order to cut the optical fibers into a uniform length, high-precision physical contact (PC) polishing is performed. The PC polishing process incurs high costs, and accordingly, the assembling cost for incorporating optical fibers into a connector increases. During the polishing type assembling, fiber guide holes for introducing optical fibers are filled with an adhesive.
On the other hand, a method and a structure of connecting an unpolished optical fiber of a single-fiber connector to a counterpart optical fiber are known. The unpolished optical fiber is pulled out in advance from the front end of the ferrule. This arrangement can prevent the optical fiber from retreating inside the ferrule due to thermal deformation of the fiber. An elastic material (a deformation absorber) is provided at the rear end of the ferrule so as to press the optical fiber. See, for example, Patent Document 2 listed below. When two ferrules are pressed against each other, the facing unpolished optical fibers come into contact and retreat inside the ferrules, while pushing and elastically deforming the elastic material until the tips of the optical fibers are aligned with the front ends of the corresponding ferrules. In order to employ this structure in a multi-core MT ferrule, the projecting lengths of multiple optical fibers are made uniform as in the polishing type connectors.
Accordingly, it is desired to provide an inexpensive optical connector that assures reliable optical connection at low loss, compensating for unevenness of the fiber projecting length, even if the polishing process of optical fibers at the front end of the ferrule is omitted after incorporation of the optical fibers.